1. Technical Field
The following description relates to a liquid crystal display (LCD) device, and more particularly, an LCD device and a driving method thereof which remove image sticking when a frame rate control (FRC) mode and an interlaced scan mode are used.
2. Discussion of the Related Art
With the advancement of various portable electronic devices, such as mobile phones, personal digital assistants (PDAs), notebook computers, etc., the demand for Flat Panel Display (FPD) devices applicable to the portable electronic devices is increasing. LCD devices, plasma display panels (PDPs), field emission display (FED) devices, and light emitting display devices are being actively researched as FPD devices.
In such FPD devices, LCD devices are devices that display an image using the optical anisotropy of liquid crystal. Since the LCD devices have a thin thickness, a small size, and low power consumption and realize a high-quality image, the LCD devices are widely used.
FIG. 1 illustrates charts for describing a state in which image sticking is caused by a polarity bias in accumulated frames, in a related art LCD device using an FRC mode and an interlaced scan mode in a related art device.
As methods of displaying an image, there are an interlaced scan mode (hereinafter, referred to as an “interlaced mode”) and a progressive scan mode (hereinafter, referred to as a “progressive mode”). The interlaced mode, in which there is a small amount of data, has been widely used, but, recently, the progressive mode is also being used more widely.
The FRC mode is a mode that reduces the number of bits of data to decrease the number of data transfer lines, and compensates for a degradation of an image quality, and is being applied to most LCD devices.
One Advanced High Performance In-Plane Switching (AH-IPS) mode is called “a fringe field switching” (FFS) mode. In the AH-IPS mode, a pixel electrode and a common electrode are formed to be separated from each other with an insulating layer therebetween. In LCD devices using the AH-IPS mode, one electrode is formed in a plate shape, the other electrode is formed in a finger shape, and an alignment of a liquid crystal layer is adjusted with a fringe field generated between the two electrodes.
In LCD devices that receive input video (generated in the interlaced mode) from an external system to output an image through a panel in the interlaced mode, image sticking is caused by the use of the interlaced mode. The image sticking excessively occurs in LCD devices driven in the AH-IPS mode. To solve this problem, various methods for removing the image sticking caused by the use of the interlaced mode are being researched and developed.
Moreover, even in the LCD devices that output an image by using the FRC mode, image sticking caused by the FRC mode occurs. The image sticking excessively occurs in the LCD devices driven in the AH-IPS mode. To solve this problem, various methods for removing the image sticking caused by the use of the interlaced mode are being researched and developed.
However, in LCD devices using both the interlaced mode and the FRC mode, image sticking caused by the interlaced mode and the FRC mode differs from image sticking occurring in LCD devices to which the interlaced mode and the FRC mode are applied separately from each other.
Therefore, even though there are a method for solving image sticking in the interlaced mode and a method for solving image sticking in the FRC mode, a method which is implemented by simply combining the two methods cannot remove image sticking occurring in the LCD devices using both the interlaced mode and the FRC mode.
The image sticking occurring in the LCD devices using both the interlaced mode and the FRC mode can occur due to various causes, and particularly, a polarity bias in accumulated frames is known as a severe cause of image sticking.
The reason that the image sticking is caused by a polarity bias in the LCD devices using both the interlaced mode and the FRC mode will now be described with reference to FIG. 1. In FIG. 1, a first line (X) indicates input images inputted as first to fourth frames in the interlaced mode, a second line (Y) indicates FRC patterns which are repeated in units of four frames, and a third line (Z) indicates panel polarities of the first to fourth frames.
A method of calculating a polarity bias in each of a plurality of pixels of a panel is expressed as the following Equation (1):
                    polarity        =                                                                                                                                                                                                                                    (                                                              input                                ⁢                                                                                                                                  ⁢                                image                                ⁢                                                                                                                                  ⁢                                of                                ⁢                                                                                                                                  ⁢                                first                                ⁢                                                                                                                                  ⁢                                frame                                ×                                FRC                                ⁢                                                                                                                                  ⁢                                pattern                                ×                                panel                                ⁢                                                                                                                                  ⁢                                polarity                                                            )                                                        +                                                                                                                                                                                                          (                                                              input                                ⁢                                                                                                                                  ⁢                                image                                ⁢                                                                                                                                  ⁢                                of                                ⁢                                                                                                                                  ⁢                                second                                ⁢                                                                                                                                  ⁢                                frame                                ×                                FRC                                ⁢                                                                                                                                  ⁢                                pattern                                ×                                panel                                ⁢                                                                                                                                  ⁢                                polarity                                                            )                                                        +                                                                                                                                                                                                                                  (                                                  input                          ⁢                                                                                                          ⁢                          image                          ⁢                                                                                                          ⁢                          of                          ⁢                                                                                                          ⁢                          third                          ⁢                                                                                                          ⁢                          frame                          ×                          FRC                          ⁢                                                                                                          ⁢                          pattern                          ×                          panel                          ⁢                                                                                                          ⁢                          polarity                                                )                                            +                                                                                                                                              (                                  input                  ⁢                                                                          ⁢                  image                  ⁢                                                                          ⁢                  of                  ⁢                                                                          ⁢                  fourth                  ⁢                                                                          ⁢                  frame                  ×                  FRC                  ⁢                                                                          ⁢                  pattern                  ×                  panel                  ⁢                                                                          ⁢                  polarity                                )                                                                        (        1        )            
A polarity of a first pixel P1 of the panel of FIG. 1 which is calculated through Equation (1) is expressed as Equation (2):polarity=(1*0*(+1))+(0*0*(−1))+(1*1*(+1))+(0*0*(−1))=1  (2)
That is, a case in which there is an input image is set to 1, a case in which there is no input image is set to 0, black in the FRC pattern is set to 0, white in the FRC pattern is set to 1, a case in which a panel polarity is negative (−) is set to −1, and a case in which a panel polarity is positive (+) is set to +1.
First, in a first pixel of the first frame, an input image is 1, the FRC pattern is 0, and a panel polarity is +1, whereby a total polarity value becomes 0.
In a first pixel of the second frame, an input image is 0, the FRC pattern is 0, and a panel polarity is −1, whereby a total polarity value becomes 0.
In a first pixel of the third frame, an input image is 1, the FRC pattern is 1, and a panel polarity is +1, whereby a total polarity value becomes 1.
In a first pixel of the fourth frame, an input image is 0, the FRC pattern is 0, and a panel polarity is −1, whereby a total polarity value becomes 0.
Therefore, a polarity of the first pixel P during the four frames becomes 1 (=0+0+1+0).
A polarity of a second pixel P2 of the panel which is calculated according to Equation (1) and the above-described method becomes 0 as expressed in Equation (3).polarity=(1*0*(+1))+(0*0*(−1))+(1*1*(+1))+(0*0*(−1))=1  (3)
Polarities of all pixels which are checked by the above-described method are as illustrated in a portion (S) of FIG. 1. That is, in the LCD devices using both the interlaced mode and the FRC mode, a polarity bias of +1 or −1 occurs in units of four frames. Such a polarity bias continuously occurs despite a frame being continued.
When the above-described polarity bias occurs, image sticking can be caused by a deterioration of the panel, and for this reason, a quality of an LCD device can be degraded.